Method of and apparatus for strip welding



March 21-, 1944. J. H. BUCKNAM ETAL 2,344,534 METHOD OF AND APPARATUS FOR STRIP WELDING INVENTORS MES H. BUCKN M JA ALFRED J. MILLE STANLEY H. ROYER ATTORNEY March 21, 1944.v

J. H. BUCKNAM ETAL METHOD OF AND APPARATUS FOR STRIP WELDING 1o sheets-sheet 2v Filed Feb. 3, 1958.

F l G. 2..

F l G. 3.

R m o u n T N m H T N D T ISEL A ERN M M MA J. H. BUCKNAM ET AL Marqh 21, 1944.

METHOD OF AND APPARATUS FOR STRIP WELDING 5 s R O m 8 2 M N A 5 m E s M v t I N e l 6 h S 0 1 Filed Feb. 5, 1958 ms ATTORN EY March 1944- J. H. BUCKNAM ET AL 2,344,534

' METHOD OF AND APPARATUS FOR STRIP WELDING Filed Feb. 3, 1938 10 Sheets-Sheet 4 INVENTORS JAMES H. BUCKNAM ALFRED J. MILLER STANLEY H. ROYER BY ATTO R N EY I March 9 4. J. H. BucKNAM ETAL 2,344,534

METHOD OF.AND APPARATUS FOR STRIP WELDING Filed Feb. 5, 1938 10 sheet s shet 5 r n H h g 2 I M I ATTORNEY March 21, 1944.

METHOD OF AND APPARATUS FOR STRIP WE LDING l0 Sheets-Sheet 6 Filed Feb. 3, 1938 IIHI! FIG. 8.

m. w 2. M 1 v m a 0 O0 0 6 8 2 d 0 M 2 H .4 8 M 8 4: 7 2 1 2 k). I \V 8 4 a M a M 2 4 K3 0 z ,1. 0 1 6 m y 8 2 a .2 a 0 0 o a 3 o 0 L 0 v E n 9 5 a 2 2 W m o 4 a a 01 O: u M w 2 6 8 t 2 M ATTO R N EY March 21, 1944. J. H. B-UCKNAM ETA-L METHOD OF AND APPARATUS FOR STRIP WELDING Filed Feb. 5, 1938 10 Sheets-Sheet 7 FIG. 13.

E H D E ATTO R N EY March 21, 1944. .1. T-LBUCKNAM ET AL METHOD OF AND APPARATUS FOR STRIP WELDING I 10 Sheets-Shee t 8 Filed Feb. 3, 1958 m FIG. 12.

INVENTORS JAMES H. BUCK NAM ALFRED J. MILLER STANLEY H. RQYER ATTORNEY March 21, 1944. .1. H. BUCKNAM ET AL 2,344,534 I METHOD GRAND APPARATUS FOR STRIP WELDING Filed Feb. :5, 1938 10- Sheets-Shet 9 MQQ s R o T N E v m ATTORN EY J. H B UCKNAM ET'AL 2,344,534

METHOD OF- AND APPARATUS FOR STRIB WELDING Filed Feb. 5, 1938 10 Sheets-Sheet 10 March 21, 1944.

ems rllo own 0. WNh

NR fin 5 v s mww Em wfi mg NR Gw QM 5% 4 wfimx Em Ew v 8% A wmd g m v a Rm 8. 4 2K Sm 3% m? 3 QR 3 W3 R ATTORNEY This invention relates to the art Patented Mar. 21, 1944 UNITED STATES PATENT OFFICE 2,344,534 I METHOD or AND APPARATUS FOR s'rmr wnmmo James H. Bucknam and Alfred J. Miller, Cranford, and. Stanley H. Boyer, Elizabeth, N. J., assignors to The Llnde Air Products Company, a corporation of Ohio Application February 3, 1938, No. 188,468

15 Claims.

of welding. More particularly, the invention concerns a method of welding metal sheets or strips into continuous strips and to an automatically controlled apparatus for performing the method.

Present day. practice in the production of sheet steel has tended steadily toward the continuous strip mill process, the successful development of which has been attained in fairly recent years. By this method, sheet steel is produced by rolling out the white hot ingot into strips varying from 20 to 100 inches in width and approximately 150 to 500 feet in length. Upon hot rolled strips are wound into coils and sen to the cold finishing mills.

,Before the cold rolling operation, the strips. are unwound, stitched together, passed through a continuous pickling bath and washed in cold correspondingly decrease the amount of handling required per ton of steel. This joint between the strips could be formed therein at sometime subsequent to the hot rolling operation and prior to the cold rolling operation and either before or after the strips are pickled and washed.

As a solution to this problem, it is proposed to provide an improved method and a novel apparatus for butt welding adjacent strips in such bets for both holding the edges of the members to be welded tightly together and for maintaining the adjacent edges of the members in alignment suitable for welding so that one edge will not be higher than the other. For proper operation, these clamping members are relatively large and must necessarily be located in the emerging from the hot finishing mills, these long,

heat zone of the weld. Due to their size and location, these large clamps rapidly conduct a great deal of heat away from the weld thereby decreasing the economy of forming the welded joint. I

To overcome this objectionable feature, th novel apparatus of the invention maintains the adjacent strip edges in tight engagement by clamps or other means which engage the strips at points considerably spaced from the line of welding; and, maintains the edges of the strips in accurate alignment for the welding operation by relatively smaller auxiliary members, such as rolls and presser feet, which are located in the heat zone of the weld. As these relatively small members located in the heat zone carry P less heat away from the weld, the economy of operation is increased; while, at the same time, the accuracy of alignment of the strip edges is increased.

It is therefore an object of this invention to provide an improved method of welding steel sheets into a single strip. Another object is to produce a new welded product. Other objects are to provide: a machine for practicing such welding; a machine capable of forming smooth joints which can remain, in the strip during the cold rolling process; a machine including separate, simultaneously operated welding units. each adapted to form a portion of the Welded joint, of a length differing from that formed by a manner that the joint mayremain in the continuous strip during the cold rolling. As one of the novel features of this improved method, it is proposed to lessen the amount of strain on thisjoint by shearing the strip edges on a taper so that the seam between adjacent strips extends diagonally across the continuous strip. When the composite strip is cold rolled, the cold rolling mills thus will engage adjacent portions of the joint successively, minimizing the tension imposed on the joint by the cold rolling operation.

Prior art machines for forming buttwelds have generally relied upon a single set of memthe other; a machine including means to maintain the strip edges in accurate alignment without conducting an excessive amount of heat from the weld; and a machine including means automatically maintaining the heat applied to the work at a uniform value, means automatically controlling the movement of each unit along the work in synchronism with the other, and means automatically interrupting the operation of each unit when its portion of the welded joint has been completed.

These and other objects of the invention will in part be obvious and in part become apparent from the following description and accompanying drawings, in which:

Fig.1 is a view, partly in front elevation and vertical sectional view, taken on .thelinel-iofliml- .4 a right hand end elevational view of a front elevational view, partly in the left hand welding unit shown iii a side elevational view, partly in secleft hand welding unit, the view from the rear of the apparatus is an enlarged longitudinal sectional illustrating the arrangement of presser feet the lower machine: Y

Pig. 7 is a perspective view of the rear end of the left hand welding unit;

Pig. 8 is a view mainly in plan of the clutch mechanism for raising and lowering the upper blowplpe, the casing being shown in section;

Hg. 0 is a side view, partly in section, of the apparatus shown in Fig.1:

Hg. 10 is a vertical sectional view through the photoelectric cell assembly;

Hg. 11 is a plan view of the motor driven valve mechanism controlling the supply of gases to the blowpipes with the cover removed;

I'ig. i2 is an end elevational view of the apparatus shown in Pig. ii;

Fig. 18 is a vertical sectional view, taken on the line lt-ll of Fig. 11. looking in the direction of the arrows: and

Figajta and 14b together constitute a wiring diagram showing the electric circuits for controlling the operation of the left hand welding unit.

Generally speaking, the improved welding method of the invention is practiced by first shearing the sheets or strips to be welded along a line which is non-perpendicular to the edges of the sheet. In practice, the sheets are generally sheared on a taper of one inch per foot out of square. The strips to be welded are then firmly clamped on a suitable supporting frame at points considerably spaced from the welding none and with their adjacent edges in tight engagement. v

In the preferred embodiment of the welding Procedure and apparatus disclosed herein, welding units are simultaneously moved in opposite directions from the outer edges of the strip toward the center, while the strip edges are held in accurate alignment by auxiliary means located in the heat-none of the weld, to form a welded Joint. It will be apparent that if the movement of the units were continued until they met at the center..a small central portion of the strip edges would not be weld united. Accordingly, the movement of one unit is automatically reversed at a predetermined point in its travel before the unit reaches the center of the strip, and the forward movement of the other unit is con-' tinued past the center of the strip and slightly past the same predetermined point to complete the welded joint.

While, for rapidity of operation. it is generally desirable to use two units simultaneously and heat both the upper and lower sides of the strip edges. the upper side of the strip edges only may be similarly heated; or the invention may be practiced by movin one unit along the entir lined method comprises a stationary supporting frame I on which the sheets or strips P to be welded are supported in proper position for welding between pairs of clamps C, C. It will be noted that the clamps C, C are each spaced from the edges to be welded so that these relativeb large members, which have extensive stationary surface engagement with the sheets P throughout substantially the full width thereof, will be far enough from the heat zone of the weld that no appreciable amount of heat will be carried from the weld by the clamps. Left and right hand welding units U and U, respectively, each comprising an upper welding machine W and a lower welding machine W, are secured to travelling supports such as slides S and 8', respectively, movable longitudinally of the frame 1' along the seam to be welded. Hydraulic cylinders H are mounted on the frame and secured to the lower clamps C for moving the latter vertically to clamp the sheets or strips P between the lower clamps C and the upper fixed clamps C.

Each welding machine W, W includes relatively small movable means having limited and progressive line contact with the sheets adjacent their abutting edges and movable heating means. The movable heating means comprises a high temperature heating medium which is preferably an oXy-fuel gas blowpipe, although other heating mediums such as an electric arc may be used. The relativelysmall movable means may comprise a pair of presser rolls engaging the sheet or strip edges on either side of the welding line and one or more presser feet directly engaging the strip edges along the welding line. The presser rolls and presser feet on the upper and lower machines of each unit cooperate to maintain the sheet or strip edges in accurate alignment for the welding operation. To, further insure a good welded Joint between the sheets or strips to be welded, one of the presser .feet on each lowermachine W- may be located directly beneath the preheat flames of the upper heating unit and be so formed that its upper edge, engagin the under side of the work has a V contourtransversely of the seam. This presser foot will thus exert an upward bending force on each of the opposed strip edges to "peak" or upset the adjacent edges of the sheets or strips slightly as they are heated. This condition is not only very desirable for uniform and economical welding but also accurately maintains the edge alignment and permits relatively wide tolerances in the preparation of the sheets or strips for welding.

To take up any excess metal present from the shearing operation, the sheets or strips P are so placed on the frame F that a loop is formed in the strips between the clamps C, C' and the presser feet and rolls. To control this loop, the

seam to be welded is disposed at a slightly higher elevation than that of the clamps C, 0'. thereby increasing the pressure with which the adjacent edges of the sheets are forced into engagement during the welding operation. This bowing or looping of the sheets or strips between the clamps and the presser elements may be accomplished is usually about ten inches and the edges to be welded are about 1% inches higher than the level of the clamps.

Also mounted upon the. frame F, as will be described in more detail hereinafter, are suitable mechanisms, such as the motors M and M, each operatively associated with one of the welding units and which actuate shafts G and G, respectively, for moving the-slides attached to the welding units, limit switches J and J' actuated, respectively, by shafts G and G, control boxes B and B, relay panel B, and photoelectric cell amplifier unit A, and motor driven valve operating mechanism V and V, the latter being carried by the welding machines W and W. Within the control boxes B and B are control circuits, each operatively associated with one of the mechanisms mentioned above and including an element or elements operative when the welding unit controlled by the circuit reaches a predetermined point in its-path of travel, to interrupt the energization of the mechanism associated with said unit. Preferably, said elements are operative in such sequence that one unit welds a greater length of the seam than the other unit.

Operation of the apparatus is controlled by push buttons and switches mounted in the control boxes B and B, one of which controls the left hand unit U and the other of which. controls the right hand unit U. The sheets or strips P to be welded are placed on the lower clamps C and fluid is admitted to the cylinders H to raise the lower clamps so that the sheets are firmly held between the upper and lower clamps with their adjacent edges in juxtaposition. When this has been accomplished, a button on the control panel is depressed to bring the upper and lower welding machines W and W, respectively, of each unit U or U, into operative relation with the work. Depression of other buttons energizes the valve operating mechanisms V and V', each controlling the supply of oxygen and a combustible gas to the upper and lower blowpipes of one unit U or U. An additional valve on each upper valve operating mechanism V- or V may, if desired, be used to control an air blast to blow the excess heat in a iorward direction from between the rolls, and a similar valve on the lower valve operating mechanism controls the flow of fluid to a water jet adjacent the under side of the weld, which water jet will be more fully described hereinafter. When the blowpipes have been lightechanother set of push buttons is depressed to close the circuits to motors M and M" to move the welding units U and U from the ends of the welding line toward the center. As left hand unit U approaches the center of the welding line, it is automatically retracted from the work, its associated motor is automatically reversed and the associated valve operating mechanisms V automatically energized to interrupt the supply of gaseous heating mixture to its blowpipes and the above mentioned air blast. This operation may be efl'ected by the limit switch J which, although shown as a single unit, comprises a plurality of switches controlling various circuits; or it may be efl'ected by another limit switch J mounted on the upper left hand slide the units. The unit U is then retracted from the sheets P, its movement similarly reversed, and the associated valve controlling mechanisms V energized to close its respective valves.

Although the apparatus is fully automatic in operation, separate controls are provided so that it may be manually operated, if desired. For instance, it is sometimes desirable to automatically control the movement of left hand unit U along the welding line and manually control the movement of right hand unit U' therealong. Such a procedure permits a very accurate control of the welding of the overlap between the units in case the length of this'portion of the seam varies dueto unforeseen circumstances. In-this instance, interference between the units is prevented by the'limit switch J" which causes reversal of the unit U when it is actuated by contacting unit U.

The penetration of the weld is either automatically or manually controlled by varying the distance between the upper blowpipes and the work, and a suitable switch is incorporated in each control box B for selecting the desired control.

Manual control is accomplished through the actuation of push buttons which complete circuits to the blowpipe moving mechanism moving this a is similar to that described in U. S. Patent No.

\ 2,089,014, issued on August 3, 1937, to J H. Buckof I the welding line to weld the overlap between varying the speed with which the blowpipe traverses the work, it is preferred to vary the distance between the blowpipe and the work. This procedure affords a more sensitive control of the quality of the weld. As the amplifying means for the photoelectric cell is similar to that described in the above-mentioned patent, only such portions of the amplifier have been shown in the drawings and described herein as are necessary to a. complete understanding of the present invention.

Another'method of accurately manually con trolling the heat applied to the weld is to provide a current meter, showing the output current reading of the photoelectric cell amplifier unit A, in a position where it may be observed by the operator. The operator, by noting the meter reading may then actuate the push buttons manually controlling the blowpipe moving mechanism to maintain the blowpipe in proper relation to the Work so that the correct amount of heat is applied to the weld at all times.

While the above apparatus has been described as controlled by a plurality of push buttons which respectively move the welding units into position, turn on the various gases to the blowpipes, and start the movement of the units, it will be obvious that this control may be simplified considerably by providing additional contacts on certain of the operating buttons whereby, it both units U and U are used simultaneously, the entire operation may be controlled by only three push buttons. In this instance the push buttons used include one button for starting 'each unit and an additional button'for-moving both units into operative relation with the work to be welded. The stopping of the units is controlled will be fully described in a later part of this,

specification. The main elements of the DP- ratus will now be described in detail.

In the embodiment of the invention selected for illustration in the drawings, and as shown in Pig. 1, the framel" may be secured at one end to a suitable support II, and at its opposite end may rest on a suitable bearing member 22. The frame consists of longitudinal members 24 and 2', cross members 2|, SI, and 32, uprights 34 and 30, and end plates 8! and 40. The hydraulic cylinders H are mounted on the members 24 and have their pistons pivotally conected at their upper ends to the clamps C which are adapted to move in guides 41 and are connected by cross members 4. The upper clamps C are rigidly connected to the uprights 34, it and to the end plate II.

A plate 40, secured to members 20, supports the left hand unit control box B, the limit switches J and J, and gearing ll for connecting the limit switches J and J' to the threaded shafts G and G, respectively. Another plate ll, secured to members 26 adjacent plate. 40, supports a hydraulic pump 12, a solenoid operated hydraulic valve l4 controlling cylinders H, and solenoid operated hydraulic valves I! and ll controlling the vertical position of the welding units U and U, respectively, relative to the welding seam. A third plate III also mounted on members II, supports the control box B for the right hand unit and the photoelectric cell amp ifv s unit-A.

Mounted on the cross members ll above th plate I and overhanging the members II is a fourth plate 82 on which are mounted relay box It, motors M and M and gear reduction unit connected to motors M and M and to vertical shafts II and Il (Fig. 4). Shafts I and II, through gear reduction units It and II, drive threaded shafts G and 0. respectively, each supportedatitsinnerandinabearing. As

shafts 88 and G, to the latter of which are operatively connected, through travelling nuts 16, the slides S; and motor M actuates slides 8' through shafts III and G, and travelling nuts II, The upper pair of slides moves on rails til (Pig. 3). extending inwardly from members 2! and the lower slides move on similar rails I! mounted on the members 24. Each slide 8 is formed with a recess 04 to accommodate shaft G and each slide 8' has a similar recess It to accommodate shaft 6.

It will be understood from the above description. that the driving shaft for the upper machine W of each unit is interlocked with the driving shaft for the lower machine W. Each motor M or M is operatively associated with a limit switch J or J, respectively, and provided with a shoe brake 88 to permit rapid reversal of the motor at the time the units U and U meet.

As the right hand unit U is identical with the left hand 'unit U, only the latter will be described in detail. and it should be understood may be seen from the drawings, motor M drives that the following description applies equally well to either unit. The unit '0, shown in detail in Figs. 5, 6, and 7, includes an upper welding machine or carriage W comprising a mounting base or plate Ill which may be bolted or otherwise secured to the upper slide 8 shown in Pig. 1. At one end, this plate is provided with a pair of spaced depending ears Ill and I, of which the ear I" is in alignment with one edge of the plate. The ear I is spaced inwardly from the opposite edge of the plate which latter is provided with a cutaway portion Hi to accommodate movement of the positioning linkage for the member W. Each ear III or I" has a bearing Ill mounted therein, which bearings support a shaft I" provided with a recess III in each end thereof and extending beyond the ears. Links I" and I" are rigidly mounted on opposite ends of the shaft I", and in the free end of each link is secured an outwardly projecting pin Ill. Each pin pivotally supports, by means of a "bearing I, a link I5 2.

the upper end of which is provided with a spring pressed detent I for at times engaging one of the recesses Ill. At their lower ends the links III are pivotally connected to one end of an upper slide plate I. Another pair oi depending ears I are formed integrally with the opposite end of the mounting plate I", and the lower ends of thue ears are pivotally connected to the opposite end of the slide plate lit. A hydraulic cylinder I" is pivotally connected to one of the depending ears Ill and the piston ofthis cylinder is pivotally connected to a pin I12 extending between the link I" and a link I'll secured to the shaft I" adjacent the ear I. When fluid is admitted into one end of the cylinder IIl, its piston will force the pin I12 outwardly to the position shown in Fig. 6, thus aligning the links I" or I" and the links I! and moving the plate I" and its attached vparts downwardly. This brings the upper machine W into operative position. When fluid is admitted into the other 'end of cylinder I10, the pin III is drawn to the right from the position shown in Pig. 6, consequently causing the plate I" to be moved upwardly by its associated links and retracting machine W from engagement with the sheets P.

In the underside of the slide plate I8! is a dovetail groove IIl formed on one side by a trapezoidal rib Ill and on the opposite side by a trapeooidal bar I" adjustably secured to the slide plate by screws I". Set screws I82, threaded into a rib I83 extending downwardly from the underside of the plate I" and provided with lock nuts Ill, engage the bar I18 to permit lateral adjustment of the width of the groove. An ear I" is formed on the underside of the plate Ill adjacent the center of the dovetail groove I'll, and secured inthis ear against axial movement, as by means of collars I88, is a shaft ill, the ends of which are threaded in opposite directions and squared as at I92. Left and right hand slide plates I84 and I88, respectively, are slidably mounted in opposite ends oi the dovetail groove I15 and each slide plate is formed at the outer end with an upwardly extending ear Ill (Pig. 5) inwhich is rigidly secured a nut 200 which engages a threaded end of the shaft I90. Rotation of the shaft I" will thus vary the spacing of the slide plates I and I" and a pair of attached squeeze rollers 2, described below. Integral with each slide plate I 54 and I is as depending arm 202 formed at its lower end into a bearing housing 284 having a passage 286 therein for the circulation of cooling fluid around the housing. A cover plate 208 is provided for each housing, and in each housing is a roller bearing 210 in which is mounted a shaft 212 on the opposite end of which shaft i secured one of the squeeze rollers 214. The axes of the shafts 212 are so arranged that the plane of each roller is at an angle to the vertical .plane through the welding unit and each roller has a frusto-conical outer bearing surface 216 in order that firm contact may be made with the members being welded.

An oval shaped plate 218 is fastened to the forward end of slide plate 166 and extends downwardly to a point adjacent the lower end of the bearing' housings 204. A shaft 222 extends through the lower end of the plate 218 and on the ends of this shaft are secured a pair of arms 224, the inner ends of which are slidably secured to the lower portions of the bearing housings 204. A press'er-foot 226 is secured to the lower end of the plate 218 ,by screws 228, and the presser-foot is provided with a passage 230 for the circulation. of cooling fluid therethrough. Conduits 100 connect each passage 206 to the passage 230 so that cooling fluid may be admitted to the passage 206 in, one housing by an inlet conduit I02, pass from there through a conduit 108 to the passage 230 and thence through the other conduit 100 to the other passage 206, from which it is exhausted. As the unit U moves along the work, the presser-foot 226 bears on the meeting edges of the sheets in cooperation with a similar foot on the lower machine W, maintaining the sheet edges in alignment for welding.

A second dovetail groove 232, formed in the underside of the plate 166 near the rear thereof, slidably receives a blowpipe slide plate 234; and a threaded shaft 286 mounted in brackets 238 secured to the plate 166 is provided with a handle .240 and threadedly engages the slide plate 234 for moving the same relatively to the plate 166. In the lower side of the plate 234 is formed a dovetail groove 242 extending at right angles to the groove 232, and in the groove 242 is mounted a slide plate 244. 'Plate 244 is formed at one end with an ear 246 in which is secured by collars 248 a threaded shaft 260 which engages the plate 234, and by means of which the plate 244 may be moved relatively to the plate 234. Slide plates 234 and 244 permit ad- .iustment of the blowpipe for the upper welding unit both longitudinally and transversely of the welding machine W, so that the blowpipe may be accurately positioned with respect to the work. A limit switch 261 is mounted on one of the ears I 68, so that a roller 252 on the free end of its actuating arm 263 will contact the movable slide plate 166 after a predetermined upward movement of the latter to control the valve operating mechanisms V associated respectively with the upper machine W and the lower machine W to close their associated valves; there: by interrupting the supply of gas to both blowp pes on the unit U.

The clutch mechanism D, which mechanically adjusts the vertical position of the upper blow: pipe with respect to the work to vary the amount of heat applied to the weld, is shown in detail in Figs. 8 and 9. This clutch mechanism comprises a base 260 and an enclosing housing 262 secured to the underside of slide plate 244 (Figs.

'6 and 7). Brackets 264 and 266, formed integral with the base 268, rotatably support a shaft268; and a double face male clutch member 210 is splined to the central portion of the shaft 268 brackets 264 and 266 aqacent one side of the base, and to the plunger 218 of each solenoid are connected links 280 and 282. One pair of links 280 is pivotally connected at its opposite end to bracket 264 and the other pair to the bracket 266. Links 282 are pivotally connected together at their opposite ends and to one arm 268 of the yoke 212. Thus, the links connected to each plunger 218 form a toggle joint between one of the brackets and the yoke 212, whereby, when the solenoid is energized, its plunger will be pulled downwardly and, as the bracket is immovable, the yoke 212 will be forced in a direction away from the bracket, moving the male clutch member 218 into engagement with either of a pair of female clutch members described below.

mounted respectively on the shafts 298 and 300 rotatably mounted in the plates 290 on either side of the shaft 288. Shafts 288 and 300 extend through the inner plate 280 and on the inner end of each shaft is a small bevel gear 802, each of which gears engages a large bevel gear 304 formed on a female clutch member 306 mounted on radial bearings on the shaft 268. The motor 284 is constantly energized when the welding unit is in operation so. that the female clutch members 306 rotate in opposite directions on the shaft 268. Accordingly, the shaft 268 may be made to rotate in one direction or'the' other dependent upon which female. clutch member 306 is engaged by male clutch member 210 through energization of one of the solenoids 264' or 216. The shaft 268 extends outwardly beyond the bracket 266, in which it is mounted by means of roller bearings 308, and on this end of the shaft is keyed a-spiral gear 310 meshing with a second spiral gear 312, which latter gear is 1 mounted on a shaft 314 extending between plates 316, formed integral with the base 260, and the bracket 266. Worm 318, formed on one end of the shaft 314, engages a worm gear 320 press fitted on a sleeve 322 internally threaded toengage a shaft 324. Lugs 826, formed on the bracket 266, retain worm gear 320 against vertical movement. Shaft 324 is formed with an upper reduced threaded portion 326 on which is secured a limit switch collar 330. A spring 332, partially surrounded by an enclosing sleeve 334, engages this collar and a washer 338 supported on the top lug 326. The slotted arm 338 of a limit switch.340, mounted on the top of the bracket 266, engages the collar 330, and opens the limit switch to interrupt the pilot circuit to deenergize the solenoids 264 and 216 when the shaft 324 reaches its limit of movement in either direction. An electrical plug-in connection for to the lower side of base I".

Shaft 824 extends through a suitable packing gland N2 in the base "I, and to its lower end isilxedlysecuredanarmlllformingpartofa bracket 8. provided on its inner face with a dovetail slot I slidablyengaging a tongue 850 formed on the side of the housing-202.

Integral with the outer face of bracket I, as best shown in Figs. 6, 8, and 9, is'an outwardly extending arm "I including a vertical lug 3 between which lug and the outer face of the bracket 8 extends a shaft 8" on which is pivotally mounted a supporting sleeve III for a blowpipe ill. An adjusting screw I" thr'eadedly engagesthearmfll andatoneendabutsalug an integral with the sleeve III to limit pivotal movement of the blowpipe III in one direction. A secondlug I, integral with the upper side of sleeve 8", is pivotally connected to an adjustable length slotted link 8; and a pin ill-formed on the end of a handle 31., which is pivotally connected to the blowpipe slide plate I, slid-,- ab y c mes in the slotted end of link I.

Rotation of handle I" in one direction pivotally retract blowpipe II! from the work, and

the above described linkage is so proportioned that it will lock the blowpipe in the retracted position until handle I'll is rotated in the opposite direction. -It will be apparent that operation of the clutch mechanism D will cause vertical movement of bracket 8 and the attached blowpipe III.

Although the outer casing {ll of the blowpipe Ill is rectangular to fit the supporting sleeve I, the blowpipe is otherwise of standard construction, and includes the usual gas mixing chambers. A. water cooled 20-iiame welding head 814 is secured to the lower end of the blowpipe by a suitable connection I12, as best shown in Fig. 6. The welding head 81 is of the type described in the copending application of J. H. Bucknam, Serial No. 728,133, filed May 29, 1934, now Patent No. 2,130,28l, issued September 13, 1938. The interior of the welding head I" is substantially hollow to permit cooling fluid to circulate therethroulh in any desired manner. while the blowpipe head 314 is shown as provided with 30 welding tips, it will be obvious that I the number of tips may be varied to suit different operating conditions.

While the blowpipe moving mechanism for the upper blowpipe has been describedabove as comprising solenoid' operated clutches and a constant speed motor, it will be obvious to those skilled in the art that a reversible motor directly connected to the blowpipe may be used in place of the solenoid controlled clutch construction.

I 2,844,584 the solenoid circuits and limit switches is secured shaft 4|! is an arm 42!, the opposite end of which is forked and lies between two U-shaped brackets l secured to the lower portion of the slide plate III. A pin 4", on which is a roller 42. engaging a recess ii in the lower side of the slide plate I", is mounted in the forked end of arm "1 and slides in the brackets I24; and a spring-pressed detent 02 mounted on one of the brackets I engages a recess in the forked end of arm in when the welding unit is in its upper position. With the above described arrangement. movement of the piston of the hydraulic cylinder will cause the welding unit to pivot about the pins 4" between its advanced and retracted po sitions.

On its upper surface. plate "I slidably sup ports a pair of bracket; 4" for transverse movement on the plate. Each bracket is provided on its under face with a dovetail groove I slidably engaging a tongue I on the plate "I. A shaft 2 is rotatably secured in a depending ear I on each of these brackets, and each shaft threadedly engages one of a pair of bosses I on the plate 8; whereby the bracket may be moved transversely of the plate "8. Each shaft 2 is provided with a square end I for engagement by suitable wrench or other tool for moving its associatedbracket l3! transversely of plate 0.

Spaced ears "I formed on the upper end of each bracket 4" support pins I on each of which is pivoted an idler roller housing 454. A shaft I is mounted on roller hearings in the free end of each housing and on the projecting As such a modification will be obvious to those skilled in the art, it has not been deemed necessary to illustrate the same in the drawings The lower welding machine or carriage W of the left hand unit U is mounted on a plate 400, bolted or otherwise secured to the lower slide 8 shown in Fig. l. A pair of upstanding arms ll! connected by a cross-member I are welded to the upper side of plate 4" and in bosses formed in the ends of these arms are secured pins 4 pivotally supporting a slide plate I. One end of a hydraulic cylinder lll is pivotally secured to an ear ll! integral with the plate I adjacent one end thereof and the piston ill of this cylinder is pivotally secured to a crank II which is welded to a shaft I ll mounted in 'pillow'bloclrs l2. fastened-to the plate I". Keyed to this end of each shaft is one of the lower idler rolls 4". Each housing is formed with a cooling fluid passage and 9. depending arm "I engaged by a pair of spring-pressed plungers I mounted in recesses "I in the brackets "I. Nuts 4" threadedly engasins the recesses I and the springs "I therein, may be used to adjust the Pr s ure with which the idler rollers 45! eng e the under side of'the sheets to be welded when the machine W' is in the operative position.

Another bracket "2 having an upper forked end "I is bolted to the forward end of plate I. A pin I'll is mounted in the forked end "I of the bracket 412 and pivotally supports the main presser foot Ill and the auxiliary presscr foot or "peaker" "I. The main presser foot 15 extends both forwardly and rearwardly of the pin 4", and the forward end is forked to receive a pin "l on which is pivotally mounted the eye ill of a rod I'll extending downwardly through an apertured ear II on the bracket 112. A spring I, surrounding the lower end of rod "I and entailing ear I and a collar ll! secured on rod ill by nut l". urges the rearward extension of foot All into engagement with the seam.

The auxiliary presser foot or "peaker" 418 is formed with spaced forwardly extending arms 4, straddling presser foot 4" and pivotally engaging the pin I'll. A plunger I, seated in a recess l'in bracket 41!. is resiliently urged upwardly into engagement with the "peaker "I by a spring "I in the recess. The upper surface of "peaker" 4" is formed with a slight V contour transversely of the strip edses so as to exert an upward bending force on each of the opposed strip edges to "peak" or upset the adjacent strip edges slightly. Both presser feet are hard surfaced as at "I.

By resiliently mounting the lower presser rolls and presser feet. the pressure exerted by these elements may be controlled. and distortion, which would occur if excessive pressure were applied to the strip edges, be prevented. Furthermore, the resilient mounting of these elements automatically compensates for variations in thick-- ness of the steel being welded.. The presser feet and idler rolls on the upper and lower machines cooperate to maintain the sheets P in accurate alignment during welding.

A cooling fluid inlettube 484 is connected to one housing 454 and conduits 455 extend between the passage in each housing and the interiorof presser feet 415 and 418, so that fluid may circulate through the housings and presser feet and.

be conducted away by tubing connected to the passage of the second housing.

Bolted to the upper side of plate 488 is a hollow bracket 500 (Fig. 7), the spaced 'arms of which extend upwardly between the idler rollers 458 and rigidly support a sleeve 502 in which is slidably mounted a blowpipe 584 of the construction commonly used'in oxy-acetylene welding. The blowpipe 504 is connected to a three-flame welding head 508, similar in construction to the welding head 314 on the upper blowpipe 552. As in the case of the upper blowpipe, the number of burner tips may be varied to best adapt the blowpipe for difierent welding conditions. A water spray block 508 for preventing the formation of craters in the weld is supported on head 505 by means of an adjustable bracket 510. The lower welding torch is not movable with respect to the slide plate 408 but is held in fixed adjustable relation thereto. c

As previously explained, the quantity of heat applied to the weld is maintained constant by varying the distance between upper blowpipe 892 and the .work. The position of the blowpipe is changed by actuation of'the clutch mechanism D, which is operated in response to changes in radiant energy emission from the under side of the weld. These energy emissions affect the photoelectric cell unit E, which controls'the clutch mechanism. The unit E is bolted or otherwise secured to the plate 408 and extends upwardly between the lower idler rolls at a point substantially in line with the line of contact of the upper and lower rolls with the sheets or strips to be welded. As shown in detail in Fig. 10, the unit E includes a housing l2 secured to the plate 408 and to which is fastened another housing 5 for the photoelectric cell 5i8. A tubular extension 5l8 extends upwardly from the housing 512 and mounted in this extension by means of rubber bushings 5.20 and 522, is a quartz rod 524. Both the housing 5l2 and the tubular extension 518 are externally wrapped with copper tubing through which cooling water is circulated to eliminate thermal disturbances on the photocell and the current produced thereby. In order to avoid confusion in the illustration of the photocell assembly, the tubing has been omitted from the drawings, particularly as its application will be immediately apparent to those skilled in the art. The upper end of the tubular extension is flanged as in 528 and secured to this flange is a water cup 528 provided with a cover 530, A water pan 532 is .justing shield in may be eliminated, and the shutter 544 modified to perform the function of the light-adjusting shield. An arm 550. is secured to the tubular extension 518 and extends outwardly and upwardly therefrom. At its. outer end, this arm is formed with a plat 552 in which are mounted the shutter-control rod 554 and the Y wiper rod 555. A radio tube socket 558 is secured to the housing for the-photoelectric cell, and suitable conduits 580 are connected the water cup for providing cooling fluid at the upper end of the quartz rod adiacent the under side of the weld.

The oxygen and acetylene supplied to the upper blowpipe 582 and the lower blowpipe 504 01 the left hand unit U are controlled by suitable regulators, the details of which form no part of the present invention. To prevent popping of the blowpipe tips when the blowpipes are operated, the supply of gas to each blowpipe is controlled by a motor driven sequence valve operating mechanism V. This type of valve mechanism, as adapted for manual actuation, is disclosed and claimed in the copending application of L. W. Young, Serial 'No. 169,921, filed October-.20, 193'! now United States Patent No. 2,187,581. The present mechanism is essentially the same as the hand actuated mechanism with the exception of necessary changes to adapt it for motor actuation and the 'addition of an air or water supply valve operated by the acetylene valve operating lever. The valve mechanism is designed toopen the oxygen valve first and close this valve last. The acetylene valve is opened after thepxygen valve has been opened and closedbefore the oxygen valve is closed. The air or water supply valve is in Figs ll, 12, and 13, includes a base 552 uponwhich is mounted a valve block 554 in which are spring closed, plunger-operated valves for the oxygen and acetylene supply. Secured tothe also secured to the flange 525 surrounding the' water cup 528. Mounted for horizontal move ment in the water cup on a shaft 534 is a wiper arm 536, provided with a rubber wiper 558 engaging the upper end of rod 524. A spring 540 surrounds the wiper arm for normally urging it to one position. A stud 542 is secured to the cover 530 and. pivotally mounted on this stud is a shutter 544 for varying the amount of light falling upon the end of the quartz rod through a tubular openbonnet 5580! the valve-block 554 is a similar valve 588-for supplying an air blast to the upper welding machine or cooling fluid to the spray block 508 on the lower machine. Upstanding ears 510 on the bonnet rotatably support a shaft 512 on which are cams 514 and 516 for operating the valves in a predetermined sequence. One end of shaft 512 is formed with a cam-518 adapted to open a limit switch 580, mounted on base 562, when all the valves are fully open or fully closed. On the opposite end of shaft 512 is loosely mounted a large spur gear 58i provided with a hub 582. The outer end of the hub is notched as at 583 and a cage 584 overhangs this outer end and is pinned to the shaft 512 as at 585. The cage 584 is radially bored as at 588 and an adjusting screw 581 is threaded in the bore. In a socket 588-in the screw 581 is a spring 585 engaging a ball 590, mounted in the inner end of bore 585, and normally urging this ball into the notch 588. The above described arrangement constitutes a slip clutch drive between gear 58l and shaft 512.

A motor 58l, mounted on the base 552, drives a small spur gear 592, engaging the gear 582, through a reductionunit 588. A spring loaded friction disc 584 is provided at the outer end of.

motor. I

An arm "I, pivoted on a shaft I mounted on the back of ixmnet ill, and which arm is engaged by cam I14, is adapted to engage the plungera of the acetylene valve and valve I.

' Another arm '91, similarly pivoted, and engaged by cam i", is adapted to engage'the plunger of the oxygen valve. A spring I" urges each arm upwardly into engagement with its associated cam.

The valve operating mechanism V operates as follows: When the motor ill is energized through a circuit closed by ap ush button on the control board 8, the shaft m and cams ill and I" are rotated in a direction to first cause the cam "I to depress arm Ill and open the oxygen valve, after which cam I'll depresses arm is! to open the acetylene valve and valve I. When the valves have all been fully opened, the cam ill on the shaft IIl actuates the limit switch "I to break the motor circuit When it is desired to close the valves, another push button on conamass the motor shaft to prevent overrunning of the,

source is continually circulated through the idler roller boll-511188. pre'sser feet, blowpipe heads and trol box 3 is depressed to complete a circuit for reversing the motor Ill. Rotation of shaft I12 and earns l", "O in the opposite direction first permits the acetylene valve and valve I" to close and then permits the oxygen valve to close. When all the valves are fully closed, cam I'll actuates limit switch I to again break the motor circuit. As may be seen from the drawings, bonnet I" is provided with suitable open lugs for the conduits I" and the electrical connections to switch "I controlling motor III. I

The purpose of the slip clutch drive is to prevent damage to the mechanism in case of overrunning of the motor "I. If the motor does not stop immediately when cam "I is at its limit of movement in either direction of rotation, ball III will ride up out of notch ill disconnecting the motor drive from the cam shaft 512. The spring I" will move ball I" into notch I" when bore 5" and notch "I again become aligned, as will occur when the motor MI is restarted.

As described at the beginning of this specificatlon, when the welding operation is about to begin. either or both of the machines W and W are moved into engagement with the sheets P by their associated hydraulic cylinders H0 and II, respectively. The valve-mechanisms V and V are then actuated to supply the gas mixture to the blowplpes I" and III, respectively, the air blast for the upper units and the supply of water to the spray block "I. However, satisfactory welds may be formed without the use of the air blast on the upper unit. When the blowpipes the copper tubing on the photocell observation unit E.

The wiring diagram represented in Figs. 14a and 14b shows the various circuits for controlling the operation of the left hand welding unit. The circuits for controlling the operation of the right hand welding unit are the same as those for the left hand unit with the exception of certain changes which will be described hereinafter. The control apparatus, as may be seen from Fig. 1, includes a control box 13, the relay panel B. and the amplifying unit A for the photoelectric cell control, all of which are mounted on the frame 1". Also mounted upon the frame F, either on separate panels or in the above listed control apparatus are the control circuits for the driving motors M and-M and for the clutch mechanism For the sake of clarity. groups of wires connected to common pieces of apparatus in Figs. 14a and 14b have been shown as a single heavy line to represent multi-conductor cables. Also, in the wiring diagram, all push buttons, switches, and relays are shown in the positions which they occupy when the welding apparatus is inoperative.

Referring now in detail to Figs. Ila and b, wires Ill extend from a suitable source of alternating current to terminals ill and "I on the terminal board T. Similarly, wires "3 connected to a suitable source of direct current, extend to terminals "4 and "I on the terminal board T. Connected to the wires in are wires 8 which extend to the right hand welding unit. Wires "1, I, III, and It I' extend, respectively, from the terminals Ill, "2, I, and "I through the line switch L tothe terminals Iii, Iii, Ill,

' and II, respectively, of the terminal board '1.

have been lighted, the upper blowpipe, through the medium of clutch mechanism D is moved vertically into proper relation with the work to be welded and the motors M, M energized to rotate shafts G, G and move either or both of slides B. 8' and units U. U from either end toward the center of the welding line. As each unit moves along the welding line, its associated photoelecsupply. When each unit has returned to its starting point, an associated limit switch deener-' gixes its driving motor M or M. During the weiding operation, cooling fluid from a suitable Thus when line switch L is closed terminals Ni and III are at A. C. bus potential and terminals ill and III at D. 0. bus potential.

From the terminals Ill and ill a pair of wires lit and Ill extend to the primary winding ill of a transformer Ill; and, from the secondary winding "I of this transformer, a pair of wires l2! and I22 extend through the terminals Ill and "I of the terminal board T to the primary winding!" of a transformer .21. The secondary winding "I of the transformer II! is connected by wires 8" and I" to opposite terminals of a copper oxide rectifier iii. A wire "2 connected to the wire III extends therefrom to the terminal "4 of the terminal board T; and a wire I" connected to wire I22 extends through terminal "I to the common connection I" of the armatures l and N4 of the motors ill for the valve operating mechanisms V controlling the supply of gas to the upper and lower blowpipes. respectively.

Another wire "0 extends from the terminal "I to the common connection "1 of the solenolds I and I" of the solenoid operated bydraulic valves it and II, and wires I and "I extend between the terminal; I and "I and the motor 2 of the clutch mechanism D, which motor is therefore continuously energized whenever the line switch L is closed. However, a limit switch may be inserted in the motor circult so that-the motoris not energized until the unit has reached the welding position, which limit switch may be operated by movement of the unit to the welding position.

To bring the welding machines W, W into position on the sheets to be welded, the operator 'switch 694 closed limit switch 614,

" g asses depresses push button 8" which energizes the relay 8 through the following circuit; termi* nal 8, wire 808, lineswitch L, wire 6", junction 848, the contacts of push button 6", wire I" and terminali", relay 8, wire 65!, junction 85!, wire 653, junction 654, wire lit and terminal H5.

When thus energized, relay N6 completes the following circuit to the solenoid 38: terminal 604, one wire "3, junction 6 58, wire 851, Junction 858, wire 9, relay arm 650, wire Bil and terminal 655, solenoid 838, junction 631, and wire 838 to terminal 605. The push button 845 should be retained in a depressed position until such time as the upper and lower welding machines W and W, respectively, are fully in position, through energization of the solenoid 838 which opens the hydraulic valve 56 to admit fluid to the hydraulic cylinders I10 and B which move the upper andlower welding machines W and W, respectively, into position on the sheets to be welded.

When the welding operation has been cmpleted, the operator, by depressing push button 682, may energize the relay 663 through a circuit similar to that described for push button which relay will in turn complete a circuit similar to that described for the relay 646 to energize the solenoid 639 which opens its associated hydraulic valve 58 to cause the hydraulic cylinders I and M0 to retract the welding machines W, W from the work.

With the welding machines in position, the operator depresses the push button 884 which completes the following circuit to energize the stick relay 685: terminal N5, wire Bill, junction 688, wire 661, relay 685, wire 668 and terminal 869; the contacts of push button 664, wire 610, junction 6", wire 612 and terminal 613, normally closed limit switch 614, wire 609 and terminal II. A holding circuit for the relay 665 is completed through its relay arm 616 as follows: junction 61], wire 818, relay arm ill, wire 810 and terminal 68!, the contacts of normally closed push button I, junction 6.82, wire 683, junction 6" and wire 612 as previously described.

Relay $65, when energized, completes the circuit for causing the motor IQI of the valvemechanism V for the upper machine W to rotate in a direction to open the oxygen and acetylene valves and valve 586 in sequence. This circuit is as follows: from one side of the secondary winding 82!! of the, transformer H8, through wire 632, junction 6", wire 686, front contact 681, wire "I, held winding 689 of the motor 59L wire "0, front contact "I, wire 692, junction 683,

closed limit switch 694, junction I02, wire 95, armature I of motor I, wire 896, junction 3, wire 8 and terminal 635 to the opposite side of the secondary winding 620 of the transformer H9. As the motor starts to rotate the limit switch"! closes and when all the valves have moved to their fully open position, the limit to the motor and stopping further operation thereof. The holding circuit for the relay 665 may be broken either by depressing the push button I or through operation of the normally which is the limit switch III operated by the upward movement of plate Ill when machine W is retracted from the sheets P at the completion of its portion of the welding operation. In either instance, when the relay 8 becomes deenergized, the following circuit is then completedior causing the motor Ill of thevalve mechanism V to rotate in the opposite direction to close its valves: from one side of secondary winding 620 of transformer H8, through wire 632 to junction 685, wire 686,

back contact 691, wire sac-,nua 689 (in the opposite direction from that heretofore described) wire 688, back contact 698, wire 692, junction J93, limit switch 103 (now in the closed position) wire see, back contact no, wire m, junctionswitch 103 opens to break the circuit for the motil is opened thus breaking the circuit tor. Push buttons "I03 and operate in conjunction with limit switch 614 and relay 108 to control the operation of the valve mechanism V for the lower machine W' in the same manneras described for the push buttons 665 and GM comtrolling relay $65 and valve operatingmechanism' V for the upper machine W.

As previously stated, automatic control of the welding is accomplished by means of a photoelectric cell observation unit E mounted on the lower welding machine W in a position to receive radiant energy from the lower side of the weld.

This photoelectric cell unit, the construction of which has been previously described, is connected to an amplifying unit A- similar to that described in U. S. Patent-No. 2,089,014, issued on August 3, 1937, to J. H. Bucknam. et al.; and from which current is taken to operate relays to cause a change in the position of the upper blowpipe 392 with respect to the welding seam. This mechanism comprises the clutch mechanism D, which, as also previously described, includes a motor 284 which operates continuously oppositely rotating female clutch members 306. Either of the oppositely rotating clutch members may be engagedby the movable male clutch member 210 to cause the upper blowpipe 392 to be raised or lowered with respect to the work, thus varying the penetration of the weld and maintaining the weld uniform. The amplifier unit A and the photocell observation unit E are shown in dotted outline in the wiring diagram. Parts of the control for clutch mechanism D may be mounted in thefor raising and lowering the upper blowpipe will now be described.

. Any variation in the welding heat froma pre- A determined normal amount will cause the photocell unit E either to increase or decrease the current output of the amplifier unit A, through the wires 10'! and 108 extending through the termirials 109 and H0 of the'terminal board T to the zero-center relay 1| l, actuating this relay I to cause its contact arm H2 to swing either to the left or to the right to engag either the contact H3 or the contact H4, respectively. If the contact arm H2 swings to the left, for instance, the relay "H5 is energized through the following circuit: from one side of the secondary winding 828 of the transformer 621 through wire 629, copper oxide rectifier -63|, wire H8 and terminals H1 switch X (which has been swung to the right to sistance 140, wire 141 and terminal 142, junction 143, wire 144 and wire 303 to terminal 314; (2) Junction 145, relay arm 143, wire 141 and terminals 143 and 143 to a light 150, and thence through junction 151 and wire 341 to wire 303 and terminal 514. The above circuit causes the light 150 to be illuminated whenever the blowpipe is in movement. The first circuit causes the relay 131 to be energized and this completes a circuit as follows: from Junction 134 (which is connected to terminal 315 as previously described) through wire 152, junction 1,53, wire 154, Junction 155, wire 153, relay arm 151, wire 153 and terminal 153, solenoid 254, junction 131, resistance,

132, wire 133 and junction 143 which, as has been previously described, is connected to terminal 314. Energization of solenoid 254 causes the male clutch member 210 to engage one of the female clutch members 303 and rotate shaft 233 in a direction to raise the blowpipe. This movement continues as long as the photoelectric cell E receives an excess of radiant energy from the weld. However, the total amount of movement of the blowpipe in either direction is limited by either of the switches 121 or 134 (which are part of the limit switch 340), for protective purposes.

If the zero-center relay 11I.had been so energized that its contact arm 112 had swung to the right to engage the contact 114, the relays 135 and 133 would have been energized to in turn cause energization of the solenoid 213 through circuits similar to those already described, and thus cause lowering of the blowpipe.

Manual control of the position of the upper blowpipe with respect to the work is accomplished through the medium of push buttons 133 and 133 which respectively control raising and lowering of the blowpipe. To condition the apparatus for manual operation the contact arm 113 of the "manual-automatic" switch X is moved to the left to engage the contact 110. To raise the blowpipe, push button 133 is depressed and closes the following circuit from contact 110 (the circuit to contact arm 113 is the same as previouslyoutlined); contact 110,

wire 111, junction 112, contacts of push button I 133, wire 113 and terminals 114 and 115, junction 113, and relay 115, the rest of the circuit being as previously described. Depression of push button 133 lowers the blowpipe through a circuit similar to that just described.

As previously described, the amount of heat applied to the weld may be maintained constant by placing a suitable meter in the output circuit of the amplifier unit A and disposing this meter a'djacentthe operator's position. The operator, by observing the reading of this meter and operating the push buttons 133 and 133 may then maintain the position of the blowpipe with relation to the work at the proper point for supplying the desired constant amount of heat to the weld.

The driving motor M for moving the weldin unit with respect to the sheets to be welded is preferably controlled by means of "forward, reverse" and stop" push buttons 111, 113, and 113, respectively, and limit switches 130, 131, 132, and 133, of which switches and 133 are normally closed and switches 131 and 132 are normally open.

Depression of the -forward" push button 111 completes the following circuits: (1) Terminal 314, wire 303, wire 341, junction 135, wire 133, contacts of stop" push button 113, wire 131, junction 133, wire 133, contacts of "forward" push button 111 and terminals 130 to one side of the "forward relay 134. From the opposite side of the relay this circuit comprises wire 131, normally closed limit switch 130, junction 315, normally closed limit switch 133, wire 132, junction 133, wire 134, wire 310 and terminal 315; (2) Terminal 315, wire 310, wire 134, junction 133, wire 135, junction 133, wire 131, the contacts of "forward" push button 111, wire 133, junction 133, wire 300 and terminal 301 and Junction 302. This circuit shunts the normally closed limit switch 183 in case the latter should be open. When relay 134 is energized, a holding circuit therefor is completed through its relay arm 303 as follows: junction 804, wire 305, relay arm 303, wire 303, junction 301, wire 303 and terminal 303, junction 138, wire 131, the contacts of stop" push button 113, wire 133, junction 135, wire 341, wire 303 and terminal 314. This holding circuit may be broken by the opening of limit switch 130 or depression of stop" push button 113.

The relay 134 energizes motor M through conventional circuits to move the welding unit U from the edges of the sheets toward the center to make the weld. When the welding unit U has moved a definite distance toward the center, limit switch 130 opens to ,open the circuit controlling relay 134 to stop forward movement of the unit U, and limit switch 131 closes to cause reverse movement of the unit through energizetion of "reverse" relay 304 as will be described below.

Depression of reverse push button 113 menually reverses the movement of the carriage through the following circuit: terminal 314, wire 603, wire 341, junction 135, wire 133, the normally closed contacts of "stop push button 113, wire 131, junction 310, wire 311, contacts of "reverse" push button 113, wire 312 and terminal 813, relay 304', wire 314, Junction 313, normally closed limit switch 133 and thence as previously described for "forward" push button 111. Depression of reverse" push button 113 completes another circuit which extends from junction 133 through the contacts of push button 113, wire 313, junction 133 and wire 300 to shunt the normally closed limit switch 133 in case the latter is open, in the same manner as previously described in connection with the depression of push button 111. Relay 304 when energized causes reverse movement of the unit U and a holdi z circuit is completed for this relay which extends from wire 312 through junction 311, wire 313, junction 313, relay arm 823 and wire 321 to junction 322 and thence as previously described for the holding circuit for relay 184. The relay 304' may also be energized through closing of the limit switch 181 which complete a circuit extending from junction 323 through wire 324, switch 181, wire 325, junction 313, wire 313,1unction 311, wire 312, and relay 304' and thence as previously described.

Depression of stop" push button 113 -stops 

